According to SPFS, a laser light is applied to the surface of a metal membrane under attenuated total reflection [ATR] conditions, and compressional waves (surface plasmons) are generated on the surface of the metal membrane in contact with a dielectric so as to increase the number of photons in the applied laser light several tens to several hundreds of times (the electric field enhancement effect by surface plasmons). In this manner, a fluorescent dye in the vicinity of the metal membrane is efficiently excited to allow for the detection of a trace amount and/or a trace concentration of an analyte.
Not only SPFS but other techniques for detecting a captured biomarker in a sample have a conventional problem in that contaminants in a sample such as blood or blood plasma inhibit the desired capturing reaction when the sample is brought into contact with a sensor area, resulting in a decrease in assay signal as well as an increase in assay blank. This problem is known to be mainly attributed to contaminants being non-specifically bound to a sensor substrate.
On the other hand, an increase in assay blank is caused also when the purity of a labeled antibody is not sufficiently high, as a result of labeled contaminants being captured by a sensor area.
Because SPFS is a system which detects a trace amount or a trace concentration as described above, there is an essential problem in that a decrease in assay signal and any increase in assay blank lead to a lowering in detection sensitivity. Further, the occurrence of any non-specific adsorption to such an extent that the resonance angle shifts causes a change in the degree of electric field enhancement in SPFS.
Patent Literature 1 discloses a biosensor for SPR measurement (SPR: surface plasmon resonance) that includes a substrate having at least a surface to which a bioactive substance has been bound and a surface (a reference section) free of bioactive substances, the reference section being protected with two or more kinds of hydrophilic groups in order to suppress non-specific adsorption to the reference section.
Patent Literature 2 discloses an SPR measurement sensor having, on the surface thereof, an active area in which ligands will be immobilized and a reference area free of the immobilization of ligands arranged in parallel to each other along the direction of an analyte flow. A difference is obtained between an active signal detected at the active area and a reference signal detected at the reference area, thereby cancelling an individual difference in measurement data between different sensors.